Multifunctional Fe₂O₃-Au Nanoparticles with Different Shapes: Enhanced Catalysis, Photothermal Effects, and Magnetic Recyclability

We investigate Au-decorated Fe₂O₃ nanoparticle catalysts, Fe₂O₃-Au, where the supporting Fe₂O₃ nanoparticles are of different shapes: spheres, rings, and tubes. The decoration procedure for the Fe₂O₃-Au nanoparticles is identical for each shape, and is analogous to the synthesis of pure Au nanoparticles (AuNPs). These similarities allows for direct comparison between the different shapes and the pure AuNPs. The morphological, optical, and magnetic characterizations reveal that the Fe₂O₃-Au nanoparticles are hybrid structures exhibiting both plasmonic and magnetic properties. The different shape Fe₂O₃-Au nanoparticles and the AuNPs are evaluated for their ability to catalytically reduce 4-nitrophenol. Remarkably, it is found that Fe₂O₃-Au nanoparticles are more efficient catalysts than AuNPs because they can achieve the same, or better, catalytic reaction rates using significantly smaller quantities of Au, which is the catalytically active material. Taking into account the Au-loadings, the Fe₂O₃ rings and tubes are superior to the Fe₂O₃ spheres as catalytic supports due to their Fe₂O₃ crystal phase. It is also shown that the Fe₂O₃-Au nanoparticles have the additional benefit for catalysis in that they can be recovered and reused via magnetic collection. Furthermore, the Fe₂O₃-Au nanoparticles and AuNPs are found to efficiently transduce heat from light through plasmonic absorbance, and this phenomenon is exploited to demonstrate the photothermal catalytic reduction of 4-nitrophenol.